The present invention relates to a seat belt retractor used for a seat belt device equipped in a vehicle such as an automobile and a gear mechanism for transmitting rotation of a spool for retracting a seat belt to other members or for transmitting rotation of other members to the spool and a seat belt device having the same.
A seat belt device attached to a vehicle seat of an automobile or the like has been provided with a seat belt retractor. The seat belt retractor locks rotation in a belt withdrawing direction of a spool for retracting a seat belt by means of an operation of a lock gear of a locking mechanism in case of emergency where a large deceleration acts on a vehicle at a collision or the like, for example.
The spool is urged by spring means in a seat belt retracting direction all the time. Thus, if an occupant disengages a tongue from a buckle when releasing the seat belt, the seat belt having been withdrawn is retracted by the spool by an urging force of the spring means relatively rapidly. When a full length of the seat belt is retracted by the spool and rotation of the spool and stopped, an inertia body supported by the lock gear so as to be capable of swing is operated by its inertia and moved to a lock position. Then, an end lock might occur, thereby preventing the rotation of the spool in the seat belt withdrawing direction by the operation of the inertia body. As a result, the seat belt cannot be withdrawn any more.
The inertia body of the locking mechanism rotates to the lock position during rapid withdrawal faster than a normal withdrawing speed of the seat belt and locks the rotation of the spool in the seat belt withdrawing direction. Also, the inertia body brought to the lock position returns to a non-lock position by a self restoring force or rotation of the spool in the seat belt retracting direction or the like.
In view of this problem, a seat belt retractor has been proposed, wherein the seat belt comprises an end-lock preventing mechanism for preventing occurrence of end lock by preventing rotation of the inertia body to the lock position by a stopper member when the full amount of the seat belt has been retracted by the spool and by controlling the stopper member by a cam operated according to a rotation amount of the spool in the seat belt retracting direction of the spool (See Japanese Unexamined Patent Application Publication No. 9-58410: Patent Document 1, for example).
Also, a seat belt device having an end-lock preventing mechanism for preventing the occurrence of end lock by another method is proposed (See Japanese Unexamined Patent Application Publication No. 2004-106561: Patent Document 2, for example). With the end-lock preventing mechanism of the seat belt device disclosed in Patent Document 2, the seat belt withdrawn from the seat belt retractor is wound around a movable pulley, and the seat belt is urged all the time by a spring through the movable pulley. By reducing a retracting speed of the seat belt by continuously reducing a bending angle of the seat belt by the movable pulley as a retracted amount of the seat belt by the spool becomes large, the occurrence of end lock is prevented.
However, in the end-lock preventing mechanism of the seat belt retractor described in Patent Document 1, it is still necessary to provide a cam operated according to a rotation amount in the seat belt retracting direction. Therefore, the number of components is large, which makes the structure complicated.
Also, in the end-lock preventing mechanism of the seat belt device described in Patent Document 2, it is still necessary to provide a movable pulley along a predetermined moving path at a position separated from the seat belt retractor. Thus, the number of assembling processes for assembling the seat belt device to a vehicle is large. Furthermore, relative positions of the seat belt retractor and the movable pulley should be positioned and assembled with high accuracy in order to obtain a certain stable deceleration of the seat belt retracting speed. Moreover, a space for ensuring movement of the movable pulley should be provided in a limited space of a vehicle body, and the structure is complicated. Thus, the seat belt retractor described in Patent Document 2 has a problem that assembling workability is not good.
Moreover, an urging force of the spring means for urging the spool is applied to the seat belt all the time, and at the same time, an urging force of the spring means for urging the movable pulley is also applied. Therefore, a large seat belt withdrawing force is required when an occupant operates to withdraw the seat belt. Therefore, handling performance by the occupant of the seat belt is not favorable. Furthermore, a sense of pressure on the occupant when the seat belt is worn is large. Particularly, since the seat belt is urged by the movable pulley in the seat belt withdrawing direction all the time, the urging force of the spring means urging the spool also needs to be large. Thus, the sense of pressure on the occupant when the seat belt is worn is further made large and adjustment of the sense of pressure on the occupant is difficult.
The present invention has been made in view of the above circumstances and has an object to provide a seat belt retractor which can simplify the structure, further facilitate assembling, improve handling performance of a seat belt by an occupant and more effectively prevent the end lock, and a seat belt device using the same.
Further objects and advantages of the invention will be apparent from the following description of the invention and the associated drawings.